1. Field of the Invention
The present invention relates to a method for producing a piezoelectric composite substrate including a plurality of piezoelectric single crystal materials and relates to a piezoelectric element including a driving electrode arranged on at least one piezoelectric single crystal material of the piezoelectric composite substrate.
2. Description of the Related Art
Piezoelectric vibrators and piezoelectric resonators each including a piezoelectric composite substrate with a single-crystal thin film made of a piezoelectric material have recently been developed. The single-crystal thin film made of a piezoelectric material has been produced by a production process including depositing a piezoelectric material, such as AlN or ZnO, using sputtering or CVD (for example, see Y. Osugi et al.; “Single Crystal FBAR with LiNbO3 and LiTaO3”, 2007 IEEE MTT-S International Microwave Symposium, pp. 873-876). The single-crystal thin film formed by the production process has a c-axis orientation in which the orientation direction of the crystal axis is aligned vertically with respect to the substrate. Thus, the performance of a piezoelectric element cannot be adjusted by controlling the inclination of the crystal axis and the polar axis.
Furthermore, a conventional production process that can control the inclination of the crystal axis and the polar axis includes polishing a single-crystal material base made of a piezoelectric material (for example, see M. Bruel; “Silicon On Insulator Material Technology”, Electronics Letters, vol. 31, Issue 14, Jul. 6, 1995, p. 1201). In this process, most of the piezoelectric material is discarded as shavings, which results in poor efficiency of utilization of the piezoelectric material. Moreover, it is difficult to provide a thin film having a uniform thickness, which causes poor productivity.
In addition, a plurality of piezoelectric materials can be thermally bonded to produce a piezoelectric element (for example, see Japanese Patent No. 3264074). In this case, after the piezoelectric materials are held and stacked, heating is performed. When the piezoelectric material is in the form of a thin film, the piezoelectric material is liable to be broken and difficult to handle, which also causes poor productivity.
When a piezoelectric composite substrate including a piezoelectric thin film bonded to another piezoelectric material is produced by a conventional production process, it is difficult to improve productivity while the crystal axis and the polar axis of a single-crystal thin film are controlled.
Furthermore, for a piezoelectric composite substrate in which a plurality of piezoelectric materials are bonded, the piezoelectric materials can be heated to locally develop pyroelectric charges on a bonding surface at the time of production, thereby damaging the bonding surface and reducing the piezoelectricity.